Conventionally, a coaxial cable configured such that an insulating layer and a shield layer are provided at the outer periphery of a center conductor has been broadly used for electronic equipment such as a mobile phone and medical equipment. Generally, the shield layer is formed from a braid or a tape wrapping. However, there is a problem that productivity is low due to an extremely-low linear velocity at the step of forming these components.
In recent years, further diameter reduction in a coaxial cable has been demanded with an increasing demand for size reduction and weight reduction in electronic equipment and medical equipment. For diameter reduction in the coaxial cable, thickness reduction in a shield layer is effective. However, there is a problem that a finished outer diameter is great in the method for forming the shield layer from a braid or a metal tape wrapping.
For this reason, the method for forming a shield layer by use of, e.g., conductive paste has been used. In the case of using the conductive paste, the shield layer is formed in such a manner that a conductor covered by an insulating layer passes through a tank filled with the conductive paste to apply the conductive paste to an insulating layer surface, and then, is squeezed in a die and dried. In this case, there might be a problem that the insulating layer is detached from the shield layer during the subsequent step of forming a sheath layer. Improvement of adhesive properties between the insulating layer and the shield layer remains as an issue.
For example, a method in which an adhesive component is mixed with conductive paste is conceivable as a solution to this problem. Moreover, a method in which a surface of an insulating layer is roughened has been also known (see Patent Literatures 1 and 2).